Acceleration control system

ABSTRACT

An acceleration control system stores a target acceleration calculation equation acquired by transforming an equation that expresses that a product of the differentiation of the square power of the speed and the environmental factor α env  represents a sensed value ε of acceleration. A surrounding environment monitor device detects surrounding bodies present in the forward periphery of the vehicle, and an environmental factor calculation unit calculates the environmental factor α env  by using the detected positions of the surrounding bodies. A target acceleration setting unit successively sets target accelerations a ref  in compliance with the target acceleration calculation equation by using the environmental factor α env . The acceleration is executed to match the driver&#39;s feeling.

CROSS REFERENCE TO RELATED APPLICATION

This application relates to and incorporates herein by referenceJapanese Patent Application No. 2007-166847 filed on Jun. 25, 2007.

FIELD OF THE INVENTION

This invention relates to an acceleration control system for controllingacceleration of a vehicle and, particularly, to an acceleration controlsystem capable of controlling the acceleration to match driver'sfeeling.

BACKGROUND OF THE INVENTION

In one conventional acceleration control system for a vehicle, when atarget speed of vehicle travel is set, vehicle acceleration control isexecuted so as to automatically assume the target speed (for example,U.S. Pat. No. 4,650,020, JP 3-76247B). According to this system,immediately after the start of control, the target speed is set at avalue higher than an actual vehicle speed by a predetermined value and,thereafter, the target speed is linearly increased. When the targetspeed is linearly increased as above, the acceleration becomes nearlyconstant.

When the vehicle is constantly accelerated up to the target speed,however, the driver often feels the controlled operation scary or findsthe controlled acceleration offensive.

In another conventional acceleration control system for a vehicle, torealize acceleration that matches driver's acceleration feeling, anacceleration characteristic is selected depending upon the individualdriver's ability and drive feeling, and the acceleration control isexecuted based on the selected acceleration characteristic (for example,JP 6-255393A).

When the acceleration is controlled by selecting an accelerationcharacteristic depending upon the individual driver's ability and drivefeeling, the acceleration characteristic must be adjusted in advance tomatch the individual driver's ability and drive feeling. This adjustingoperation is cumbersome and, besides, a number of accelerationcharacteristics must be provided.

SUMMARY OF THE INVENTION

This invention has an object of providing an acceleration control systemcapable of easily controlling acceleration to match driver's feeling.

According to a study, it was found that a visually recognized change inposition of objects around a vehicle dominantly affects the accelerationfeeling perceived by a driver. This acceleration feeling sensed by thedriver was quantized by using the tau theory, which specifies the motionof an object body based on a change in the retinal image. As a result,it was found that if the acceleration feeling sensed by the driverchanges, a differentiated value divided by a square power of visualinformation τ (hereinafter simply referred to as τ) that represents thepassing of time, too. Further it was found that the differentiated valuedivided by the square power of τ remains constant, if the accelerationfeeling sensed by the driver is constant.

In order to achieve the above object, according to a first aspect, anacceleration control system successively detects positions ofsurrounding bodies present in the periphery of the vehicle but in frontrelative to the vehicle. The acceleration control system determines thetarget acceleration based upon the following (1) to (5), i.e., (1) thefollowing Equation (Eq.) 1 expressing a relation among τ_(S) whichrepresents, based on visual information, the time until a surroundingbody in front of the vehicle comes in contact with the driver, anangular velocity u of the surrounding body with the driver as areference, and τ which represents, based on visual information, theelapse of time until the surrounding body passes by the side of thevehicle, (2) the following Equation 2 between the differentiation of1/τ² and a sensed value ε of acceleration numerically expressing thedriver's acceleration feeling, (3) the following Equation 3 expressing arelation among τ_(S), a distance r from the vehicle to the surroundingbody, and a differentiated value of the distance r, (4) a relativeposition of the surrounding body detected by the surrounding bodydetection device, and (5) a sensed value so of preset targetacceleration used as the input value ε for the Equation 2.

$\begin{matrix}{\tau = \frac{\tau_{s}}{1 + {u^{2}\tau_{s}^{2}}}} & {{Eq}.\mspace{14mu} 1} \\{{\frac{\mathbb{d}}{\mathbb{d}t}\frac{1}{\tau^{2}}} = ɛ} & {{Eq}.\mspace{14mu} 2} \\{\tau_{s} = {- \frac{r}{\overset{.}{r}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

If the acceleration feeling sensed by the driver changes, adifferentiated value divided by the square power of τ varies. To give adesired acceleration feeling to the driver, therefore, the accelerationmay be so controlled that the differentiated value divided by the squarepower of τ assumes a predetermined value. Therefore, the accelerationsensed by the driver is expressed by a numerical value ε, and theEquation 2 of ε and the differentiated value divided by the square powerof τ is used for determining the target acceleration. As expressed bythe Equation 1, further, τ can be represented by τ_(S) and the angularvelocity u of the surrounding body and as expressed by the Equation 3,τ_(S) can be expressed by the distance r up to the surrounding body anda differentiated value of the distance r (i.e., relative speed of thesurrounding body). Therefore, the target acceleration is determined byusing a position of the surrounding body relative to the vehicle, theabove Equations 1 to 3 and the sensed value ε₀ of target acceleration.The torque of a prime mover is controlled so as to assume the targetacceleration and can realize the acceleration that matches the driver'sfeeling. Besides, the acceleration characteristic does not have to beadjusted in advance, and the acceleration can be easily controlled.

In addition to the above finding, it was also found through ageometrical calculation that the left side of the Equation 2, i.e., thedifferentiated value divided by the square power of τ is equal to adifferentiated value of the square power of the speed multiplied by anenvironmental factor.

According to a second aspect, an acceleration control system detects thepositions of surrounding bodies present in the periphery of the vehiclebut in front on a polar coordinate system with the vehicle as a centerand the line in the back-and-forth direction of the vehicle as aninitial line. When a value based on visual information on a passing time(elapse of time) until the surrounding body present in front of thevehicle passes by the side of the vehicle is denoted by τ, theacceleration control system determines an environmental factor that is acoefficient of the differentiated term of the square power of the speedbased on the position of the surrounding body in the following Equation4 between the differentiated value divided by the square power of τ andthe differentiation of the square power of the speed. The accelerationcontrol system stores the following Equation 5 between the right side ofthe Equation 4 and the sensed value ε of acceleration numericallyexpressing the driver's acceleration feeling or an equation transformedfrom the Equation 5 as a target acceleration calculation equation, anddetermines the target acceleration by substituting the environmentalfactor determined by the environmental factor calculation means, sensedvalue ε₀ of a preset target acceleration and the current vehicle speedfor the target acceleration calculation equation.

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}t}\frac{1}{\tau^{2}}} = {\frac{\cos^{2}\phi}{r^{2}}{\left( {1 + {\tan^{2}\phi}} \right)^{2} \cdot \frac{\mathbb{d}v^{2}}{\mathbb{d}t}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

where r is a distance from the vehicle to the surrounding body, φ is anangle of the surrounding body in the polar coordinate system, v is aspeed of the surrounding body and t is a time,

$\begin{matrix}{{{\alpha_{env} \cdot \frac{\mathbb{d}v^{2}}{\mathbb{d}t}} = ɛ}{where}{\alpha_{env} = {\frac{\cos^{2}\phi}{r^{2}}\left( {1 + {\tan^{2}\phi}} \right)^{2}}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

The right side of the Equation 4 is transformed from the left sidethrough a geometrical calculation. The Equation 5 is acquired from theEquations 2, 4.

The sensed value ε₀ of target acceleration is variously set to set atarget acceleration depending upon the acceleration feeling sensed bythe driver, and the torque of the prime mover is controlled based on thetarget acceleration. Therefore, the acceleration can be realized tomatch the driver's feeling. In the case of the second aspect, too, theacceleration characteristic does not have to be adjusted in advance, andthe acceleration can be easily controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagrammatic view illustrating a body on a polar coordinatesystem with a vehicle as a center and a line in the back-and-forthdirection of the vehicle as an initial line;

FIG. 2 is a diagrammatic view of the polar coordinate system as viewedfrom the side direction of a vehicle;

FIG. 3 is a diagram showing Equations in the step of transforming adifferentiated value divided by a square power of τ into adifferentiation of a square power of speed;

FIG. 4 is a graph illustrating a relation between time of accelerationby a driver so that the intensity of acceleration feeling remainsconstant and a differentiated value of 1/τ²;

FIG. 5 is a graph schematically illustrating relations between time ofdriving that the acceleration feeling remains constant and a rate ofchange of 1/τ² in the cases of large, intermediate and smallacceleration feelings;

FIG. 6 is a block diagram illustrating an acceleration control systemaccording to an embodiment of the invention;

FIG. 7 is a view illustrating results of calculating the magnitudes ofdifferentiated values of 1/τ² for various regions in front of thevehicle;

FIG. 8 is a block diagram illustrating a travel control unit used in theembodiment shown in FIG. 6; and

FIG. 9 is a flowchart illustrating major portions of control executed inthe embodiment shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a vehicle 10 and a body 12 are illustrated asexisting on a polar coordinate system (R, θ) with the vehicle 10 as acenter and a line in the back-and-forth direction of the vehicle as aninitial line (X-axis).

<Equations 1 and 3>

In the Equation 1, τ (tau) is a value that represents, based on visualinformation, the time until the body 12 passes by the side of thevehicle and is often referred to as τ of passage to distinguish it fromτ_(S). The other τ_(S) is a value that represents, based on visualinformation, the time until the body 12 comes in contact with the driverwho is driving the vehicle 10 and is often referred to as τ of contactto distinguish it from τ of passage. The visual information inclusive ofboth τ of passage and τ (=τ_(S)) of contact stands for optical fluidityof the body 12 imaged on the retina.

The above Equation 3 expresses τ_(S) with an axis passing through thebody 12 as an R-axis. Further, the above Equation 1 expressing τ ofpassage based on τ and the angular velocity u of the body 12 is a knownrelational expression that can be determined from a geometrical relationshown in FIG. 1.

In FIG. 2, the vehicle 10 is shown in the polar coordinate system (R, θ)as viewed from the side direction. As will be understood from FIGS. 1and 2, the R-axis which is a polar axis is an axis in a solid(three-dimensional) space.

<Equation 4>

From FIG. 1, τ_(S) and the angular velocity u can be expressed by theEquations 6 and 7 by using the distance r, velocity V and angle φ,

$\begin{matrix}{\tau_{s} = {{- \frac{r}{\overset{.}{r}}} = {- \frac{r}{V\;\cos\;\phi}}}} & {{Eq}.\mspace{14mu} 6} \\{u = {\overset{.}{\phi} = \frac{V\;\sin\;\phi}{r}}} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

By substituting the Equations 6 and 7 for the Equation 1, τ of passagecan be expressed by the following Equation 8,

$\begin{matrix}\begin{matrix}{\tau = \frac{\tau_{s}}{1 + {u^{2}\tau_{s}^{2}}}} \\{= \frac{- \frac{r}{V\;\cos\;\phi}}{1 + {\left( \frac{V\;\sin\;\phi}{r} \right)^{2}\left( \frac{r}{V\;\cos\;\phi} \right)^{2}}}} \\{= {\frac{- 1}{1 + {\tan^{2}\phi}}\left( \frac{r}{V\;\cos\;\phi} \right)}}\end{matrix} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

Therefore, 1 divided by the square power of τ of passage is expressed bythe Equation 9,

$\begin{matrix}{\frac{1}{\tau^{2}} = {{- \frac{V^{2}\cos^{2}\phi}{r^{2}}}\left( {1 + {\tan^{2}\phi}} \right)^{2}}} & {{Eq}.\mspace{14mu} 9}\end{matrix}$

If a differentiated value divided by the square power of τ of passage iscalculated according to the Equation 9, transformations are successivelyacquired as defined in FIG. 3. As a result, the above Equation 4 isacquired,

$\begin{matrix}{{\frac{\mathbb{d}\;}{\mathbb{d}t}\frac{1}{\tau^{2}}} = {\frac{\cos^{2}\phi}{r^{2}}{\left( {1 + {\tan^{2}\phi}} \right)^{2} \cdot \frac{\mathbb{d}v^{2}}{\mathbb{d}t}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

In the Equation 4, the coefficient of the differentiated term of thesquare power of the speed (dv²/dt) is an environmental factor α_(env).That is, the environmental factor α_(env) can be expressed by theEquation 10, and the differentiated value divided by the square power ofτ expressed by the Equation 4 is a value that varies depending upon theenvironmental factor α_(env).

$\begin{matrix}{\alpha_{env} = {\frac{\cos^{2}\phi}{r^{2}}\left( {1 + {\tan^{2}\phi}} \right)^{2}}} & {{Eq}.\mspace{14mu} 10}\end{matrix}$<Equation 2>

A graph of FIG. 4 shows a relation between the time of when the driverhas operated the accelerator by himself so that the intensity ofacceleration feeling remains constant and d(1/τ²)/dt, that is, thedifferentiated value of 1/τ². In a state where the accelerator isoperated so that the acceleration feeling remains constant as shown inFIG. 4, it will be learned that the rate of change of 1/τ² remainsnearly constant except the rising period (e.g., 0 to 10 seconds) at thestart of acceleration.

As shown in FIG. 5, the rate of change of 1/τ², that is, thedifferentiated value of 1/τ² changes in accordance with large,intermediate and small acceleration feelings. The rate of change of 1/τ²however remains constant, if the acceleration feeling remains constantdespite the acceleration feeling is different. It will be furtherlearned that the rate of change of 1/τ² varies depending upon themagnitude of acceleration feeling.

Embodiment

Next, an embodiment of an acceleration control system will be describedwith reference to FIG. 6. In a control system 100, a cruise controlswitch 102 is operable by a driver to instruct the turn on/off of acruise control. The cruise control is for automatically accelerating thevehicle up to a target speed, and after the target speed is reached, thetarget speed is maintained. When the control switch 102 is operated, acontrol signal is output to a target acceleration setting unit 114 andto a travel control unit 120 to instruct the turn on/off of the cruisecontrol.

An acceleration feeling setting switch 103 is a switch for setting themagnitude of acceleration feeling desired by the driver, and any one of,for example, large, intermediate or small acceleration feeling can beset. A setpoint value of the acceleration feeling setting switch 103 isfed to a target acceleration setting unit 114. A target speed settingdevice 104 is operated by the driver for setting a target speed Ve, andfeeds a signal representing the target speed Ve that is set to a targetacceleration setting unit 114.

A surrounding environment monitor device 106 is a signal-acquiringdevice for acquiring signals of bodies present in the vicinity of thevehicle 10 but in front, and successively acquires the signals atregular intervals. Though the embodiment uses a camera, a radar such asa millimeter wave radar may be also used. The range in which the signalsare acquired by the surrounding environment monitor device 106 mayinclude part of a region in front of the vehicle and is, desirably,nearly equal to the visual field of the driver.

A polar coordinate system position calculation unit 108 analyzes thesignals acquired by the surrounding environment monitor device 106 andoperates the positions of the surrounding bodies present in theperiphery of the vehicle 10 and in front. The calculated positions areon the polar coordinate system (R, θ) with the vehicle 10 as a centerand the line in the back-and-forth direction of the vehicle as aninitial line.

The polar coordinate system position calculation unit 108 operates thepositions of solid bodies present on a road and in the vicinity thereof.In this embodiment, further, positions of planar bodies, too, areoperated. Planar bodies include, for example, part or whole of a roadsign drawn on the surface of the road. Further, part of the texture ofthe road surface or the whole of the texture may be regarded as thebody.

Which bodies should be operated for their positions can be variouslyset. In this embodiment, however, a plurality of portions in thesignal-acquiring range (i.e., imaging range) are set in advance asposition calculation regions, and positions of the bodies present on aplurality of position calculation regions are calculated. Further, theplurality of position calculation regions are so set as to be uniformlydispersed in the visual field of the driver.

An environmental factor calculation unit 110 successively calculatesenvironmental factors α_(env) expressed by the Equation 10 and outputsthe calculated environmental factors α_(env) to the target accelerationsetting unit 114. However, the environmental factors α_(n) (n is thenumber of the position calculation regions, i.e., the number of thebodies to be detected) are calculated from the Equation 10 for aplurality of bodies 12 of which the positions are calculated by thepolar coordinate system position calculation unit 108. An average valueof the environmental factors α_(n), i.e., the following Equation 11 isused as an environmental factor α_(env) to be output to the targetacceleration setting unit 114,

$\begin{matrix}{\alpha_{env} = \frac{\sum{\alpha_{n}\left( {r,\theta} \right)}}{N}} & {{Eq}.\mspace{14mu} 11}\end{matrix}$

Described below is why the average value of the environmental factorsα_(n) is used as the environmental factor α_(env). FIG. 7 is a viewillustrating the results of calculating the magnitudes of differentiatedvalues of 1/τ² for various regions in front of the vehicle. In FIG. 7,square frames represent the positions where the differentiated values of1/τ² are calculated. Segments extending from the square frames in a barshape represent, by lengths, the magnitudes of the differentiated valuesof 1/τ² calculated at the calculation positions. As will be understoodfrom FIG. 7, the differentiated values of 1/τ² are small in the regionsin front of the vehicle but the differentiated values of 1/τ² increasetoward the periphery. It is, on the other hand, considered that thedriver is perceiving the acceleration feeling from the entire flow ofthe visual field. In this embodiment, therefore, the average value ofthe environmental factors α_(n) is used as the environmental factorα_(env).

A vehicle motion detection device 112 is the device for detecting thecurrent speed V_(cur) of the vehicle 10, and operates to successivelydetect the positions by using a wheel speed sensor or a GPS in order todetect the vehicle speed from a change in the position with the passageof time. The current vehicle speed V_(cur) detected by the vehiclemotion detection device 112 is output to the target acceleration settingunit 114 and to the travel control unit 120.

The target acceleration setting unit 114 stores the following Equation12 as a target acceleration calculation equation, and sets a targetacceleration a_(ref) from when a control signal (control start signal)for instructing the turn on of cruise control is fed from the controlswitch 102 until a control signal (control stop signal) for instructingthe turn off of cruise control is fed.

First, the target accelerations a_(ref) are successively determined byusing the Equation 12 until the current speed V_(cur) becomes equal tothe target speed Ve set by the target speed setting device 104. Afterthe current speed V_(cur) has become equal to the target speed Ve, thetarget accelerations a_(ref) are successively determined for executingthe constant speed control (for instance PID control).

$\begin{matrix}{a_{ref} = \frac{ɛ_{0}}{2\;{\alpha_{env} \cdot v_{cur}}}} & {{Eq}.\mspace{14mu} 12}\end{matrix}$

The following Equation 5 is acquired from the Equations 2 and 4. TheEquation 5 is expanded to acquire the Equation 13. V dot ({dot over(v)}) in the Equation 13 represents acceleration. By transforming theEquation 13 into an equation of v dot, the Equation 12 is acquired.

$\begin{matrix}{{{\alpha_{env} \cdot \frac{\mathbb{d}v^{2}}{\mathbb{d}t}} = ɛ}{where}{\alpha_{env} = {\frac{\cos^{2}\phi}{r^{2}}\left( {1 + {\tan^{2}\phi}} \right)^{2}}}} & {{Eq}.\mspace{14mu} 5} \\{{2\;{\alpha_{env} \cdot v \cdot \overset{.}{v}}} = ɛ} & {{Eq}.\mspace{14mu} 13}\end{matrix}$

To determine the target acceleration a_(ref), a sensed value ε₀ oftarget acceleration is determined to be a value that corresponds to asignal from the acceleration feeling setting switch 103 by using anacceleration feeling value setting map that has been stored in advance.The determined sensed value ε₀ of target acceleration, the environmentalfactor α_(env) fed from the environmental factor calculation unit 110and the current speed V_(cur) fed from the vehicle motion detectiondevice 112 are substituted for the Equation 12 to determine the targetacceleration a_(ref).

The travel control unit 120 operates a torque instruction valueaccording to a target acceleration a_(ref) formed by the targetacceleration setting unit 114 from when a control signal (control startsignal) for instructing the turn on of cruise control is fed from thecontrol switch 102 until when a control signal (control stop signal) forinstructing the turn off of cruise control is fed. Thereafter, thetorque of the prime mover (engine or motor) is controlled based on theoperated torque instruction value.

The travel control unit 120 is shown in FIG. 8 in a functional blockdiagram. The target acceleration a_(ref) is input to a multiplier 121where it is multiplied by a gain K_(F) to calculate a target powerF_(ref). The gain K_(F) is a value set in advance by taking the weightof vehicle and the like into consideration. An actual power calculationunit 122 calculates the actual power of the vehicle 10 by using thecurrent speed V_(cur) and a transfer function s·K_(F). A differencebetween the target power F_(ref) and the actual power is calculated asan estimated disturbance. After high-frequency components are removed bya low-pass filter 123, the estimated disturbance calculated above isadded to the target power F_(ref). The value after added is output as atorque instruction value.

Next, major portions of control in the acceleration control system 100will be described by using a flowchart shown in FIG. 9. In FIG. 9, S30is processing in the environmental factor calculation unit 110, S80 andS90 are processing in the travel control unit 120, and other S areprocessing in the target acceleration setting unit 114.

At S10, first, it is checked by a control signal if an accelerationinstruction is received. If a control start signal is fed, the cruisecontrol is turned on to execute the acceleration until the target speedVe is attained. It is therefore determined that an accelerationinstruction is received if the control start signal is fed from thecontrol switch 102 to the target acceleration setting unit 114. If it isdetermined that the acceleration instruction is received (YES), theroutine proceeds to S20. If it is determined that the no accelerationinstruction is received (NO), the checking at S10 is repeated.

At S20, the target speed Ve is acquired from the target speed settingdevice 104. Next S30 is processing by the environmental factorcalculation unit 110 as described above and by which the environmentalfactor α_(env) expressed by the Equation 11 is calculated from thepositions of the plurality of bodies 12 operated by the polar coordinatesystem position calculation unit 108.

At next S40, the current speed V_(cur) is acquired from the vehiclemotion detection device 112. At S50, it is checked whether the currentspeed V_(cur) acquired at S40 is smaller than the target speed Veacquired at S20. If the determination is affirmative (YES), the routineproceeds to S60 where the target acceleration a_(ref) is calculated forconstant speed control (cruise control). The constant speed control is aPID control which calculates the target acceleration a_(ref) accordingto the following Equation 14 wherein K_(P), K_(D) and K_(I) are presetgains,

$\begin{matrix}{a_{ref} = {\left( {K_{P} + {sK}_{D} + \frac{K_{I}}{s}} \right) \cdot \left( {V_{e} - V_{cur}} \right)}} & {{Eq}.\mspace{14mu} 14}\end{matrix}$

If the determination at S50 is negative (NO), on the other hand, theroutine proceeds to S70 where the target acceleration a_(ref) iscalculated for acceleration control. That is, the sensed value ε₀ oftarget acceleration is determined to be a value that corresponds to asignal from the acceleration feeling setting switch 103. The thusdecided sensed value ε₀ of target acceleration, the environmental factorα_(env) calculated at S30 and the current speed V_(cur) acquired at S40are substituted for the above Equation 12 to thereby calculate thetarget acceleration a_(ref).

After having executed S60 or S70, S80 is executed. S80 is processing inthe travel control unit 120 which calculates the target power F_(ref)from the target acceleration a_(ref) as described above, calculates theactual power from the current speed V_(cur), regards a differencetherebetween as an estimated disturbance, and calculates a torqueinstruction value by adding the estimated disturbance thereto. At S90,the torque instruction value calculated at S80 is output to the primemover of the vehicle for a travel control.

At S100, it is checked whether a control stop instruction is issued,i.e., if a control stop signal is fed from the control switch 102 to thetarget acceleration setting unit 114. If the determination is negative(NO), the routine returns back to S40 above. In this case, therefore,the current speed V_(cur) is acquired again, and the target accelerationa_(ref) is calculated again by using the current speed V_(cur) that isacquired again. If the determination at S100 is affirmative (YES), theroutine ends. In this case, the cruise control ends.

As described above, the acceleration control system 100 stores thetarget acceleration calculation equation (Equation 12) acquired bytransforming the Equation 5 which expresses that a product of thedifferentiation of the square power of the speed and the environmentalfactor α_(env) becomes the sensed value ε of acceleration. Thesurrounding bodies 12 present in the periphery of the vehicle but infront are actually detected, the environmental factor α_(env) iscalculated from the detected positions of the surrounding bodies 12, andthe target accelerations a_(ref) are successively formed in compliancewith the target acceleration calculation equation (Equation 12) by usingthe calculated environmental factor α_(env). Therefore, the accelerationcan be controlled to match the driver's feeling. Besides, theacceleration characteristic does not have to be adjusted in advance, andthe acceleration can be easily controlled.

Further, the acceleration control system 100 detects the positions of aplurality of surrounding bodies 12 and determines the environmentalfactors α_(env) based on the positions of the plurality of surroundingbodies 12. Therefore, the acceleration can be controlled to furthermatch the driver's feeling.

It should be noted that the invention is not limited to the aboveembodiment only and many modifications may be implemented.

For example, the environmental factor α_(env) may be repetitivelycalculated at regular intervals during the acceleration control of thecruise control, and the target acceleration a_(ref) may be calculated byusing the latest environmental factor α_(env).

Further, when it is determined that the acceleration instruction isissued, the acceleration control system 100 readily executes theacceleration control by using the target acceleration a_(ref) calculatedby using the Equation 12. In the initial stage of acceleration, however,the acceleration may be controlled by using another target acceleration(e.g., a constant acceleration) instead of controlling the accelerationby using the target acceleration a_(ref). In this case, the accelerationcontrol by the target acceleration a_(ref) is executed after, forexample, a predetermined period of time has passed from the start ofacceleration.

Further, though the acceleration control system 100 of the aboveembodiment has calculated the environmental factor α_(env) from thepositions of the plurality of surrounding bodies 12, it is alsoallowable to calculate the environmental factor α_(env) from theposition of one surrounding body 12.

The acceleration control system 100 executes the acceleration controlwhile maintaining the sensed value ε₀ of target acceleration constant.However, the sensed value ε₀ of target acceleration may be varied duringthe acceleration. For example, if the sensed value ε₀ of targetacceleration is further increased in the latter half of acceleration,then the driver can feel the acceleration that boosts in the latterhalf. Thus, upon varying the sensed value ε₀ of target accelerationduring the acceleration, the driver can feel various kinds ofacceleration that he likes.

1. An acceleration control system for setting a target speed andperforming acceleration control of a vehicle based on the target speedand a current speed, the acceleration control system comprising: asurrounding body detection device for successively detecting relativepositions of surrounding bodies present in a front outside periphery ofthe vehicle; means for calculating, based upon the following Equations 1to 3, a target acceleration from the relative position of thesurrounding body detected by the surrounding body detection device and apreset target acceleration sensed value ε₀ which is used as a sensedvalue ε of acceleration defined by the Equation 2, wherein the Equation1 expresses a relation among τ_(s) which represents, based on visualinformation, time until a surrounding body in front of the vehicle comesin contact with a driver, an angular velocity u of the surrounding bodyrelative to the driver as a reference, and τ which represents, based onvisual information, an elapse of time until the surrounding body passesby a side of the vehicle, wherein the Equation 2 expresses a relationbetween differentiation of 1/τ² and the sensed value ε of accelerationwhich numerically expresses a driver's acceleration feeling, and theEquation 3 expresses a relation among τ_(s), distance r from the vehicleto the surrounding body and a differentiated of the distance r; andmeans for controlling torque of a prime mover of the vehicle so as toattain the target acceleration determined by the calculating means,$\begin{matrix}{\tau = \frac{\tau_{s}}{1 + {u^{2}\tau_{s}^{2}}}} & \left( {{Equation}\mspace{14mu} 1} \right) \\{{\frac{\mathbb{d}}{\mathbb{d}t}\frac{1}{\tau^{2}}} = ɛ} & \left( {{Equation}\mspace{14mu} 2} \right) \\{\tau_{s} = {- {\frac{r}{\overset{.}{r}}.}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$
 2. The acceleration control system according to claim 1,wherein the calculating means successively determines targetaccelerations while maintaining constant the target acceleration sensedvalue ε₀.